Android backbutton

[niqt]

I'm making simple examples with Qt 5.1 for android, but i have noted that with the backbutton the app exit instead of come back at previous stack page. Will be it also in future version? I think that is very important to have native behaviour (without trick).

[Moster]

I think 5.1 is more like a beta suport for android. Some essential stuff like camera and full sensor support is missing (some are working though).
I guess Qt5.2 will be awesome

[flaviomarcio]

This is true, but I'll tell you alpha version 4.1 was better than qt5.1 for android, was more stable

[martin_ky]

Hi there. The back button functionality works nicely in the Qt 5.1 developer preview without need for any tricks and behaves "according to specification":http://developer.android.com/reference/android/app/Activity.html (scroll to onKeyDown method).

According to Android documentation, the back button event is delivered via Activity.onKeyUp() which is translated as QEvent::KeyRelease with key code Qt::Key_Back.

To prevent your app from quitting, you have to handle (accept) this event. For example, in QML you would do something like this:

@
Rectangle {
focus: true // important - otherwise we'll get no key events

Keys.onReleased: {
    if (event.key == Qt.Key_Back) {
        console.log("Back button captured - wunderbar !")
        event.accepted = true
    }
}

}
@

If you want to handle it on C++ level, override keyReleaseEvent() of your main Window and do the same in there.

That being said, how you implement the "come back at previous stack page" is entirely up to you.

[LangstoniusRex]

Thanks for explaining :) It is a bit odd that it somehow works its way to quit.

[erik.ridderby]

I managed to catch the android back button in QML:

@ApplicationWindow {
onClosing: {
close.accepted = false
if (contextMenuManager.menuVisible)
contextMenuManager.menuVisible = false
}
}@

[Rizzer]

Keys.onReleased catches the Android back button in some instances.

It doesn't seem to work with ListView though. focus must be directed somewhere where I haven't anticipated.

Here is a sample main.qml with a ListView, which does not catch the Android back button:
@
import QtQuick 2.3
import QtQuick.Controls 1.2
import QtQuick.Layouts 1.1

ApplicationWindow {
id: appWindow
visible: true
width: 640
height: 480
title: qsTr("Hello World")

ListModel {
    id: longModel

    Component.onCompleted: {
        for ( var i=1; i<=100; i++ )
            append({"testName": i})
    }
}


ListView {
    anchors.fill: parent
    id: listView
    model: longModel

    delegate:
        Rectangle {
            height: 80
        width: parent.width

        Text {
            id: textComponent
            text: testName
        }
        Keys.onReleased: {
            if (event.matches(StandardKey.Back)) {
                console.log("back caught by delegate");
                event.accepted = true;
            }
        }
    }

    focus: true
    Keys.onReleased: {
        if (event.matches(StandardKey.Back)) {
            console.log("back caught by listview");
            event.accepted = true;
        }
    }

}

}
@

[Rizzer]

Keys.onReleased catches the Android back button in some instances.

It doesn't seem to work with ListView though. focus must be directed somewhere where I haven't anticipated.

Here is a sample main.qml with a ListView, which does not catch the Android back button:
@
import QtQuick 2.3
import QtQuick.Controls 1.2
import QtQuick.Layouts 1.1

ApplicationWindow {
id: appWindow
visible: true
width: 640
height: 480
title: qsTr("Hello World")

ListModel {
    id: longModel

    Component.onCompleted: {
        for ( var i=1; i<=100; i++ )
            append({"testName": i})
    }
}


ListView {
    anchors.fill: parent
    id: listView
    model: longModel

    delegate:
        Rectangle {
            height: 80
        width: parent.width

        Text {
            id: textComponent
            text: testName
        }
        Keys.onReleased: {
            if (event.matches(StandardKey.Back)) {
                console.log("back caught by delegate");
                event.accepted = true;
            }
        }
    }

    focus: true
    Keys.onReleased: {
        if (event.matches(StandardKey.Back)) {
            console.log("back caught by listview");
            event.accepted = true;
        }
    }

}

}
@

[Mr_Ada]

Can someone post a C++ version of this? I have tried to convert it and I am still not seeing the back key.

Never mind.... Here is a C++ version I was able to get to work....

@
#include <QDebug>

// regular MainWindow stuff...

void MainWindow::keyPressEvent (QKeyEvent* event) {

if (event->key () == Qt::Key_Back)
qDebug () << "<<keyPressEvent>> " <<
"[[Back button]]";
else if (event->key () == Qt::Key_HomePage)
qDebug () << "<<keyPressEvent>> " <<
"[[Home button]]";
else if (event->key () == Qt::Key_Menu)
qDebug () << "<<keyPressEvent>> " <<
"[[Menu button]]";
else if (event->key () == Qt::Key_unknown)
qDebug () << "<<keyPressEvent>> " <<
"[[Unknown button]]";
event->accept ();
}
@

[Mr_Ada]

Can someone post a C++ version of this? I have tried to convert it and I am still not seeing the back key.

Never mind.... Here is a C++ version I was able to get to work....

@
#include <QDebug>

// regular MainWindow stuff...

void MainWindow::keyPressEvent (QKeyEvent* event) {

if (event->key () == Qt::Key_Back)
qDebug () << "<<keyPressEvent>> " <<
"[[Back button]]";
else if (event->key () == Qt::Key_HomePage)
qDebug () << "<<keyPressEvent>> " <<
"[[Home button]]";
else if (event->key () == Qt::Key_Menu)
qDebug () << "<<keyPressEvent>> " <<
"[[Menu button]]";
else if (event->key () == Qt::Key_unknown)
qDebug () << "<<keyPressEvent>> " <<
"[[Unknown button]]";
event->accept ();
}
@

[OE0214]

on Android, I did this:

void MainWindow::keyPressEvent(QKeyEvent *event)
{
	if (event->key() == Qt::Key_Back)
		qDebug() << "[[Back button]]";
	else if (event->key() == Qt::Key_Menu)
		qDebug() << "[[Menu button]]";
	else if (event->key() == Qt::Key_TopMenu)
		qDebug() << "[[Top menu button]]";
	else
		qDebug() << "[[some other button]]";

	event->accept();
}

I get a debug message for the back button, but not for the menu button...I also tried Qt::Key_TopMenu, but still nothing

nor do I get the "some other button" debug message when the menu button is pressed, so this method is not even being called when I press the menu button

this message must be handled somewhere else

can anyone help?

Thanks

[uCampaign]

In Qt 5.4.2 this is what i use and it works fine:

ApplicationWindow {
....
onClosing: {
if (Qt.platform.os == "android") {
close.accepted = false;
if (stack.depth > 1) stack.pop();
}
}
}

[bbaker]

C++ code. Gives the desired/standard effect on Android. Use a QWidget with a QStackedLayout in the main window.

    stackedLayout = new QStackedLayout;
    QWidget *c = new QWidget();
    first = new FirstForm(this );

    stackedLayout->addWidget( first );

    c->setLayout( stackedLayout );
    setCentralWidget( c );

Override the closeEvent in the header:

protected:
    void closeEvent(QCloseEvent *event);

Implement the code in the body:

void MainWindow::closeEvent(QCloseEvent *event) {

if( stackedLayout->currentIndex() > 0 ) {
    QWidget *top = stackedLayout->currentWidget();
    stackedLayout->removeWidget( top );

    event->ignore();
}

}

// QED